ABSTRACT: Six strains of Nodularia spp., both toxic and non-toxic, were tested for their ability to incorporate leucine and thymidine. All axenic cyanobacterial strains studied showed high leucine incorporation (1.4 to 12 pmol μgchl
a-1 h-1 at a concentration of 212 nM leucine), whereas thymidine was either taken up at a very low rate or not at all (0 to 0.2 pmol μgchl a-1 h-1 at a concentration of 121 nM thymidine). We
therefore recommend using the thymidine incorporation method instead of that of leucine for measuring heterotrophic bacterial production during cyanobacterial blooms.